This invention relates to energetic organic compounds and more particularly to halo- and nitroalkyl dichloroformals.
U.S Pat. No. 3,306,939, entitled "Orthoesters of 2,2,2-Trinitroethanol," which issued to Marion E. Hill on Feb. 28, 1967, suggests bis(2,2,2-trinitroethyl) dichloroformal as a transitory intermediate in the synthesis of trinitroethyl orthocarbonate from 2,2,2-trinitroethanol and carbon tetrachloride in the presence of ferric chloride. The dichloroformal was neither isolated nor actually identified. Given the reactivity of the dichloroformal under those conditions, the method is unsuitable for the synthesis of bis(polynitroalkyl) dichloroformals.
Two methods for the preparation of polynitroethyl dichloroformals are described by W. H. Gilligan in U.S. patent application Ser. No. 256,462 which was filed on Mar. 30, 1981. The first method involves refluxing a thionocarbonate of the formula (RCH.sub.2 O).sub.2 C.dbd.S (where R .dbd.--C(NO.sub.2).sub.3,--CF(NO.sub.2).sub.2,--CCl(NO.sub.2).sub.2,--C(NO .sub.2).sub.2 CH.sub.3, --CCl.sub.3, --CF.sub.3, and --CF.sub.2 C.sub.3) with sulfuryl chloride in the presence of a Friedel-Crafts catalyst such as AlCl.sub.3 or TiCl.sub.4. This method has the disadvantage that stringent reaction conditions (refluxing sulfuryl chloride at 70.degree. C. for 5 days) are required. The best yields are approximately 70%, but often yields are substantially lower since the reaction is sensitive to the choice of catalyst.
The second method for the preparation of polynitroethyl dichloroformals is treatment of the thionocarbonate with gaseous chlorine in a mixture of a chlorinated hydrocarbon and a polar additive (such as trifluoroethanol or acetonitrile). Although the polar additives are necessary for reaction to occur, they can cause problems due to their involvement in side reactions. Trifluoroethanol can react with dichloroformals (I) to give mixed 2:2 orthocarbonates (II). ##STR1## Thus care must be taken to minimize this side reaction by keeping reaction temperatures between 15.degree. and 25.degree. C. Care must also be taken during the isolation of the dichloroformal product to avoid formation of appreciable amounts of the mixed 2:2 orthocarbonate. This appreciable side reaction not only lowers the yield, but causes difficulty in the isolation of the pure dichloroformal. When acetonitrile is employed as the polar additive, side reactions can also occur. Upon prolonged exposure to the sulfur chloride byproducts formed in the reaction, acetonitrile reacts to give a black polymeric substance which cannot be removed from the dichloroformal. Thus it is critical to closely monitor reaction times to avoid formation of appreciable amounts of this impurity.
Therefore, it would be desirable to provide an improved method of preparing halo-, nitro-, and halonitroalkyl dichloroformals.